1. Field of the Invention
The invention relates to hybrid laminated unidirectional fiber sheets, and assemblies thereof, having utility for impact absorption, ballistic resistance and penetration resistance per se, as well as in spall shields, structural composites and other applications.
2. Description of the Related Art
The construction of body armor for personal protection is an ancient but not archaic art. Metal armor, already well known to the Egyptians by 1500 B.C., persisted in use until about the end of the 17th century. In recent times, body armor has again become practical through the discovery of new strong fibers such as aramids, high molecular weight polyethylene, and polybenzazoles.
Various fiber-reinforced constructions are known for use in impact-resistant, ballistic-resistant and penetration-resistant articles such as helmets, panels, and vests. These articles display varying degrees of resistance to penetration by impact from knives or projectiles such as BB's, bullets, shells, shrapnel, glass fragments and the like. Ballistic-resistant and/or penetration-resistant articles which include high strength fibers made from materials such as high molecular weight polyethylene, aramids and polybenzazoles are known. See, e.g., U.S. Pat. Nos. 6,534,426, 6,475,936, and a 1984 publication of E.I. duPont De Nemours International S.A. entitled “Lightweight Composite Hard Armor Non Apparel Systems with T-963 3300 dtex DuPont Kevlar 29 Fibre.” Such articles are said to be either flexible or rigid depending on the nature of their construction and the materials employed.
Body armor is typically formed from layers of woven fabrics or non-woven sheets of fibers that are plied together. The fibers in a non-woven sheet may be unidirectionally oriented or felted in random orientation. Unidirectional fiber sheets generally contain a matrix resin to stabilize the structure. Successive sheets are rotated relative to one another, for example at angles of 0°/90° or 0°/45°/90°/45°/0° or at other angles. To construct rigid composites of this type, individual sheets are bonded together using heat and pressure to adhere the matrix in each sheet, forming a bond between them, and consolidating the whole into a unitary article.
U.S. Pat. No. 4,623,574, discloses composites comprising a network of fibers embedded in an elastomeric matrix.
U.S. Pat. No. 5,677,029 discloses a flexible, penetration-resistant composite comprising at least one fibrous layer comprised of a network of strong fibers, and at least one continuous polymeric layer coextensive with, and at least partially bound to a surface of one of the fibrous layers.
U.S. Pat. No. 5,552,208 discloses a ballistic resistant article comprised of a high strength fiber network in a matrix and a second matrix material in the form of a film which is adjacent to at least one side of the matrix-impregnated fiber network.
U.S. Pat. No. 6,119,575 discloses a body armor containing at least one ply of aromatic fibers in a first matrix, at least one ply of a woven fabric and at least one ply of polyolefin fibers in a second matrix.
U.S. Pat. No. 6,147,018 discloses hybrid protective composites made from at least one layer of woven polybenzoxazole (PBO) or polybenzothiazole (PBT) fibers and at least one layer of a fiber network of another polymer.
U.S. Pat. No. 6,162,746 discloses hybrid protective composites made from a plurality of layers of woven PBO or PBT fibers, a plurality of ballistic layers which may be non-woven unidirectional fibers, and a plurality of tightly woven layers.
U.S. Pat. No. 6,138,275 discloses a body armor comprising a flexible penetration-resistant layer backed up by a flexible impact-absorbing layer of plastic material.
U.S. Patent Publication 2003/0037361 A1 discloses a ballistic vest containing a stack of flexible woven fabrics and a stack of flexible unidirectional layers.
International Application WO 01/96111 A1 discloses a composite material comprising fabrics selected from para-aramides, high performance polyethylene and PBO, and a thermoplastic polymeric material applied to both major faces of the fabric material.
In a different area, U.S. Patent Publication 2003/0110733 A1 discloses a hybrid fabric for structural reinforcement having a first fiber with a first ultimate strain and a second fiber with a second ultimate strain greater than the first ultimate strain.
Each of the constructions cited above represented progress toward the goals to which they were directed. However, none described the specific constructions of the laminates and assemblies of this invention, and none satisfied all of the needs met by this invention.
The earlier constructions had several disadvantages. Cross-plied unidirectional fiber composites generally have better ballistic resistance and are lower weight than woven fabrics made from the same fiber type; however, they are typically more costly to produce and thus, more expensive. One continuing need is a means of reducing the cost of protective materials.
A related need recognizes that high strength fibers are intrinsically expensive and are also used in other applications such as ropes, commercial fishing nets, tire cord and a variety of reinforced plastic products, both military and civilian. In times when military demands are high, production capacity may not meet all needs. Because strong fibers are produced by complex processes, capacity cannot be quickly increased. A need exists to more efficiently utilize the limited supply of high strength fibers.
Additionally, each of the different high strength fibers used in protective materials such as armor has different characteristics against higher speed and lower speed projectiles. Protective materials having a more uniform response to different threats would increase reliability and safety.